@despina.mina,
Not possible to add captcha as of now. Might consider in later versions.
@despinamina,
To add captcha in Email Subscribers form, follow these steps:
1. Update Email Subscribers to the latest version.
2. Setup Email Subscribers with free plugin Rainmaker by following steps from here : How to use Rainmaker’s form in Email Subscribers.
3. Add captcha to your form by following steps from here : How to enable captcha in your form.
